Boron alloy steel



Patented Nov. 15, 1938 UNITED STATES PATENT orrlce BORON AIELOY STEEL Anthony G. de Golyer, New York, N. Y.

No Drawing. Application July 9, 1936,

f Serial No. 89,775

1 1 Claim. (c1. 15-126) in general use contain tungsten as the principal alloying element; the standard 18-4-1 high 10 speed steel being substantially an allow of iron with 18% tungsten, 4% chromium, 1% vanadium, 0.50% to 0.75% carbon and minor percentages of other elements, such as manganesersilicon, phosphorus and sulphur. For some uses the com- 15 position is varied by increasing or decreasing the percentage of tungsten, or of oneor more of the other elements. In some cases molybdenum or uranium are substituted for a minor portion of the tungsten. r i The improvement of one or more of the important properties and characteristics, as well as economy in the cost of manufacture, of high speed steel have been the objectives of extensive research, and various compositions have been sug- 25 gested. One heretofore proposed composition contains approximately four times as much molybdenum as tungsten; the amounts commercially used usually being from 6% to 8% molybdenum and from 1.5% to 2% tungsten. Another 30 previously proposed composition contains molybdenum as the principal alloy element, and is free from or substantially free from tungsten.

' The class of alloy tool steel containing a higher percentage of molybdenum than tungsten offers 85 certain manufacturing difiiculties which are well known. One major deficiency of this type of alloy is that molybdenum carbide, the hard constituent of the steel, is readily oxidized at temperatures generated in the tip of high speed cut- 40 ting tools, or to which the steel is subjected for heat treatment, with the result that the outer portions of the steel are rapidly decarburized. This results in a marked decrease in the hardness of the tool, and consequent loss of cutting 5 efliciency.

In the heretofore known type of alloy tool steel in which tungsten has been entirely replaced by molybdenum the decarburizing action is evenmore rapid than when a minor percentage of 50 tungsten is present. Furthermore, it has been conclusively determined by investigations extending over a period of several years that the cutting efliciency of high speed steel containing, molybdenum and free from tungsten is, in general, appreciably lower than that of the 18-4-1 tungsten type. This is further confirmed by the fact that only a limited quantity of such steels have been used commercially" since they were introduced more than ten years ago.

The objective of the present invention is to pro- 6 vide an alloy tool steel containing molybdenum and entirely free from tungsten which has advantageous physical properties and characteristics, and which possesses an average cutting efilciency superior to that of the l8-41 tungsten type, and 10 other heretofore known alloy tool steels.

I have found that by alloying appreciable amounts of boron and zirconium in steel containing molybdenum and entirely free from tungsten that I can produce an alloy tool steel which is superior to previously known high speed steels. The use of steel ofthe-present invention on numerous and widely varied industrial applications has demonstrated that it is not only fully adapted for general purposes, but that it is distinctly superior to othenheretofore-known types of steel for the cutting and working of many metals and alloys under many special and dimcult conditions. f

I have discovered that the addition of boron and zirconiinn as essential components in the steel results in the formation of hard molybdenum compounds, probably in the nature of complex constituents containing molybdenum, carbon and.

,boron; or molybdenum, carbon and zirconium; or

molybdenum, boron and zirconium, with or without carbon. I have found that such molybdenum constituents are exceptionally stable at temperatures" generated in the tips of metal cutting tools operated at high speeds, and at temperatures I necessary for thermal treatment of the steel. As a result of extensive-research I have found that the presence of appreciable amounts of boron and zirconium, as specified herein, in steel containing molybdenum, prevents decarburization of such steel during operating and manufacturing operations. J

The ease with which molybdenum carbide is oxidized at elevated temperatures in heretofore known steels ofiers serious difliculties during the cogging and rolling, as well as during subsequent thermal treatment of the steels. Such steel will frequently be decarburized to a depth of oneeighth of an inch or more. The formation of this soft skin or layer renders it diflicult or impossible 5 to heat treat tools and other articles which have been previously formed to an exact gauge. By utilizing boron and zirconium in the manner and amounts specified herein the occurrence of such decarburized, soft layers is entirely avoided. 1

The essential components of the alloy of my present invention are molybdenum, boron, zirconium, chromium, vanadium, carbon and iron. Manganese and silicon are usually present, but the amount of either of these elements in the steel should not exceed approximately 1%. Likewise phosphorus and sulphur, as well as various other elements commonly found in alloy steels, are present in the nature of impurities incidental to manufacture. It will be understood thatthe amounts of such impurities should not exceed the maximum limits usual in, alloy tool steels.

The alloy of the present invention comprises molybdenum 6% to 16%, boron 0.20% to 2.50%, zirconium 0.25% to 5%, chromium 2% to 6%, vanadium 0.50% to 3.00%, carbon 0.10% to 0.90% and the balance substantially iron.

. The results of numerous tests under controlled conditions and in regular manufacturing operations prove that the alloy of the present invention possesses greater cutting efiiciency than any previously known high speed steel. For example, tools of this alloy have from 90% to 150%. greater cutting efficiency than steels of the 18-4-1 type and from 100% to 400% greater cutting efiiciency than heretofore known high speed steels containing molybdenum as the principal alloy component. tage is apparently due to the presence of efiective amounts'of boron and zirconium in combination with the other essential components of the alloy.

Undoubtedly the chief cause for failure of high speed metal cutting tools, during operation, is the formation of a "crater at the tool tip. Such craters are apparently caused by abrasion of hot metal chips produced by the cutting tool flowing This outstanding advanover the tool tip. I have found that the combined presence of boron and zirconium in the present alloy acts to greatly retard cratering; hence, the cutting tip of the tool is maintained in better physical condition for a much longer period of time than is possible with other alloy steels.

Thealloy may be used in the as-cast condition but inasmuch as it can be readily forged or otherwise mechanically worked, I usually prefer to employ it in the wrought condition. Also, the alloy in the wrought condition is particularly amenable to thermal treatment by means of which the hardness and other physical properties and characteristics may be fixed and closely controlled over a relatively wide range.

Although the greatest scope of usefulness for this alloy appears to be in wrought forms as cutting tools, wearing parts, etc., I have found that the alloy is also valuable for welding. That is, the composition may be formed into a weld rod of any suitable type and applied by various means of fusion welding to form a deposit having susbtantially the same composition as the original alloy. Such weld deposits may be advantageously used for tips of cutting tools, wearing surfaces and the like; and may be utilized in the as-welded condition, or subjected to suitable thermal treatment before being used.

I claim: An alloy consisting of molybdenum 6% to 16%, boron 0.25% to 2.50%, zirconium 0.25% to 5%, chromium 2% to 6%, vanadium 0.50% to 3%, carbon 0.10% to 0.90%, the balance substantially iron.

ANTHONY G. DE GOLYER. 

